Development of an Organic Table Grape Production and Market in Switzerland

In Switzerland there is an increasing consumer demand for residue-free, organic table grapes. The organic cultivation of table grapes, however, is very delicate in humid climates and experience to advice organic growers is still lacking. The goal of our project that has started in 2004 is to develop and establish a cultivation system for organic table grapes under Swiss climatic and economic conditions with a high yield security and fulfilling the high quality demands of the market. Preliminary results: Interesting cultivars to produce are e.g. Fanny, Lilla, Palatina. However they are disease susceptible and must be produced under a rain roof. Better suited cultivars still need to be found. Consumer acceptance for organic table grapes produced in Switzerland is very positive. However changes towards new cultivars and lower production costs are necessary. Spray programs to achieve sufficient disease protection and no spray blotch seem to be realizable, mainly for production under rain roof

Predicting the Growth of Many Droplets During Vapor-Diffusion-Driven Dropwise Condensation Experiments Using the Point Sink Superposition Method

Water vapor present in humid air will condense in the form of many small droplets on a cooled substrate. After nucleation, the diffusion of vapor from the environment to the droplets dominates their growth by condensation, and therefore, all droplets must compete for the vapor available in the surroundings. Models that assume droplets grow in isolation or as an equivalent film poorly capture their interaction during vapor-diffusion-driven condensation and do not correspond with experimental condensation rates. By treating the droplets as point sinks, the interaction between all droplets in a system can be captured by superposing the vapor distributions of each droplet. This paper presents direct comparisons of condensation rates measured in experiments and predicted with a point sink superposition method. The results indicate that it is critical to consider a large number of interacting droplets to accurately predict the condensation behavior. Even though the intensity of the interaction between droplets decreases sharply with their separation distance, droplets located relatively far away from a given droplet must be considered to accurately predict its condensation rate, due to the large aggregate effect of all such far away droplets. By considering an appropriate number of interacting droplets in a system, the point sink superposition method is able to predict experimental condensation rates to within 5%

A note on compactly generated co-t-structures

The idea of a co-t-structure is almost "dual" to that of a t-structure, but with some important differences. This note establishes co-t-structure analogues of Beligiannis and Reiten's corresponding results on compactly generated t-structures.Comment: 10 pages; details added to proofs, small correction in the main resul

A Point Sink Superposition Method for Predicting Droplet Interaction Effects During Vapor-Diffusion-Driven Dropwise Condensation in Humid Air

During dropwise condensation from the ambient environment, water vapor present in air must diffuse to the surface of each droplet. The spatial distribution of water vapor in the local surroundings of each individual droplet determines the total condensation rate. However, available models for dropwise condensation in humid air assume that such systems of droplets grow either as an equivalent film or that the growth of each droplet is completely isolated; the interactions between droplets are poorly described and, consequently, predictions of total condensation rates may mismatch experimental observations. This paper presents a reduced-order analytical method to calculate the condensation rate of each individual droplet within a group of droplets on a surface by resolving the vapor concentration field in the surrounding air. A point sink superposition method is used to account for the interaction between droplets without requiring solution of the diffusion equation for a full three-dimensional domain containing all of the droplets. For a simplified scenario containing two neighboring condensing droplets, the rates of growth are studied as a function of the inter-droplet distance and the relative droplet size. For representative systems of condensing droplets on a surface, the total condensation rates predicted by the reducedorder model match numerical simulations to within 15%. The results show that assuming droplets grow as an equivalent film or in a completely isolated manner can severely overpredict condensation rates

A Compliant Microstructured Thermal Interface Material for Dry and Pluggable Interfaces

Thermal interface materials (TIMs), such as thermal pastes and pads, can successfully enhance contact thermal conductance by filling the gaps caused by the surface nonflatness and roughness. However, there is still an unaddressed demand for TIMs which can be applied to pluggable or reworkable interfaces in electronic systems, such as in opto-electronic transceiver modules. Reducing the contact thermal resistances at these interfaces has become increasingly important as device power density increases. These applications require dry contact interfaces that can offer the required thermal conductance under a low pressure and endure repeated mechanical compression and shear. We present a compliant metallized finned zig zag micro-spring array, as a low-cost dry TIM, that allows conformal interface contact at low pressures (~10s to 100s of kPa) by effectively accommodating surface nonflatness at a rate of a few µm per kPa. Experimental characterization of the mechanical compliance and thermal resistance confirm that this dry TIM can achieve conformal thermal contact between nonflat mating surfaces under low pressures. The total insertion thermal resistance of this dry TIM, even when mating to nonflat surfaces, is comparable to that of a polished and flat metal-to-metal contact. Mechanical compression and shear cycling tests are performed to assess the durability

Topology Optimization of Microchannel Heat Sinks using a Homogenization Approach

Topology optimization for heat sink devices typically relies on penalization methods to ensure the fi- nal designs are composed of strictly solid or open regions. In this work, we formulate a homogenization approach wherein the partial densities are physically represented as porous microstructures. This formu- lation allows design of thermal management components that have sub-grid features and leverages ad- ditive manufacturing techniques that can produce such partially porous regions within the build volume. Topology optimization of a liquid-cooled microchannel heat sink is presented for a hotspot over a uniform background heat input. The partial densities are represented as arrays of pin fins with varying gap sizes to achieve sub-grid-resolution features. To this end, the pin fins are modeled as a porous medium with volume-averaged effective properties. Height-averaged two-dimensional flow and non-equilibrium ther- mal models for porous media are developed for transport in the pin fin array. Through multi-objective optimization, the hydraulic and the thermal performance of the topologically optimized designs is inves- tigated. The pin fin thickness is chosen based on the minimum reliable printing feature size of state-of- the-art direct metal laser sintering machines, and the gap sizes between the pin fins are optimized. The resulting topologies have porous-membrane-like designs where the liquid is transported through a fractal network of open, low-hydraulic-resistance manifold pathways and then forced across tightly spaced ar- rays of pin fins for effective heat transfer. The effects of the grid resolution and the initial design guess on the resulting topologies and performances are reported. The topologically optimized designs are revealed to offer significant performance improvements relative to the benchmark, a straight microchannel heat sink with features optimized under the same multi-objective cost function. The work demonstrates that representing partial densities as porous microstructures results in nearly resolution-independent perfor- mance at sufficiently-small grid sizes through the use of sub-grid features

The Effect of Relative Humidity on Dropwise Condensation Dynamics

Dropwise condensation of atmospheric water vapor is important in multiple practical engineering applications. The roles of environmental factors and surface morphology/chemistry on the condensation dynamics need to be better understood to enable efficient water-harvesting, dehumidification, and other psychrometric processes. Systems and surfaces that may promote faster condensation rates and self-shedding of condensate droplets could lead to improved mass transfer rates and higher water yields in harvesting applications. In the present study, experiments are performed in a facility that allows visualization of the condensation process on a vertically oriented, hydrophobic surface at a controlled relative humidity and surface subcooling temperature. The distribution and growth of water droplets are monitored across the surface at different relative humidities (45%, 50%, 55%, and 70%) at a constant surface subcooling temperature of 15 C below the ambient temperature (20 C). The droplet growth dynamics exhibits a strong dependency on relative humidity in the early stages during which there is a large population of small droplets on the surface and single droplet growth dominates over coalescence effects. At later stages, the dynamics of droplet growth is insensitive to relative humidity due to the dominance of coalescence effects. The overall volumetric rate of condensation on the surface is also assessed as a function of time and ambient relative humidity. Low relative humidity conditions not only slow the absolute rate of condensation, but also prolong an initial transient regime over which the condensation rate remains significantly below the steady-state value

A super-analogue of Kontsevich's theorem on graph homology

In this paper we will prove a super-analogue of a well-known result by Kontsevich which states that the homology of a certain complex which is generated by isomorphism classes of oriented graphs can be calculated as the Lie algebra homology of an infinite-dimensional Lie algebra of symplectic vector fields.Comment: 15 page